Polymeric nanocomposites have demonstrated great potential for constructing physically flexible large area optoelectronic devices that can remain photo-active over a wide spectral bandwidth, depending on the customizable constituents. They bolster the prospect of developing ultra fast, sensitive and superior optical counterparts of the corresponding electronic devices. With the successful integration of inorganic quantum dots (QDs) in conjugated polymeric matrices (Greenham et al., Phys. Rev. B. 54:17628 (1996); Ginger et al., Phys. Rev. B. 59:10622 (1999); Huynh et al., Science 295:2425 (2002); and Selmarten et al., J. Phys. Chem. B. 109:15927 (2005)), efficient photodetection at different ranges of the electromagnetic spectrum has been realized (Qi et al., Appl. Phys. Lett. 86:093103 (2005); McDonald et al., Nat. Mater 4:138 (2005); Maria et al., Appl. Phys. Lett. 87:213112 (2005); and Choudhury et al., Adv. Funct. Mater 15:751 (2005)). This is enabled by the occurrence of tunable optical absorption and emission of the QDs (Steckel et al., Adv. Mater. 15:1862 (2003); and Bakueva et al., Appl. Phys. Lett. 82:2895 (2003)) by virtue of quantum size effect and also by the fact that they can often preserve their optoelectronic integrity within a host matrix. The quantum dots should have appreciable absorption cross-section at the excitation wavelength in order to generate excitons with good quantum efficiency (Ellingson et al., Nano Lett. 5:865 (2005)). The photogenerated excitons should disintegrate into free charge carriers at a competitively higher rate than excitonic recombination. Next, these charge carriers should be extracted from the photoconverter before they relax. To realize efficient photon conversion, the rates of photogenerated carrier separation, interfacial transfer across the different contacts, their transport through the matrix and subsequent collection at the electrodes must all be fast enough compared to exciton recombination (Nozik, A. J., Inorg. Chem. 44:6893 (2005)). Therefore, it is imperative to provide means within the nanocomposite for an efficient transport of charges by incorporating compatible constituents that would facilitate the process.
In studying photoconducting devices using conjugated polymers, electron accepting materials such as C60 and single-wall carbon nanotube (SWNT) have been utilized in some of the past studies (Yu et al., Science 270:1789 (1995); Halls et al., Appl. Phys. Lett. 68:3120 (1996); Neupane et al., Appl. Phys. Lett. 86:221908 (2005); Rahman et al., J. Am. Chem. Soc. 127:10051 (2005); and Kymakis et al., J. Appl. Phys. 93:1764 (2003)). SWNT is a fascinating material for several peculiar physical properties. Envisioned as a rolled up graphene sheet capped with fullerene like structures, it becomes a metal or a semiconductor as a function of the wrapping angle of the sheet and diameter of the nanotube (Yu et al., Science 270:1789 (1995); Halls et al., Appl. Phys. Lett. 68:3120 (1996); Neupane et al., Appl. Phys. Lett. 86:221908 (2005); Rahman et al., J. Am. Chem. Soc. 127:10051 (2005); Kymakis et al., J. Appl. Phys. 93:1764 (2003); and Odom et al., Nature 391:62 (1998)). In the metallic state (Frank et al., Science 280:1744 (1998); Bachtold et al., Phys. Rev. Lett. 84:6082 (2000); and Thess et al., Science 273:483 (1996)), SWNT is a good ballistic conductor with a supported current density at least an order of magnitude higher than that in copper wires of the same diameter (Kreupl et al., Condensed Matter, 0412537:683 (2004); and Kreupl et al., Microelectronic Engineering 64:399 (2002)). Because of its good mechanical property, high elastic modulus and high optical transparency, SWNT has been used in constructing large area transmissive films (Wu et al., Science 305:1273 (2004)), making it an ideal component for electrical coupling in futuristic photonic devices.
Carbon nanotubes have been extensively studied for their peculiar structure-dependent mechanical and electronic properties. High elastic modulus and optical transparency, extremely high aspect ratios, large surface area, and excellent transport properties have prompted their use in transistors, fuel-cells, molecular computers and light-harvesting assemblies. Recent studies have proven that metallic SWNTs can act as ballistic conductors carrying current densities that are orders of magnitude larger than copper wires of same diameter. Colloidal semiconductor quantum dots, on the other hand, are nanometer sized inorganic particles possessing size-tunable electronic and optical properties by virtue of quantum confinement of the photoexcited excitons. Due to the precise wavelength tuning (for both absorption and emission), high photogeneration efficiency, and resistance to photobleaching, semiconductor QDs show great promise for futuristic photonic applications, such as hybrid optoelectronic devices, in vivo biosensing and solar cells. Despite their immense potential, the efficiencies of hybrid polymer-QD devices fall short by almost an order of magnitude compared to their conventional inorganic counterparts. The primary reason for the relative inefficiency of the QD devices is the inefficient transfer of charge carriers to and from the photosensitive QDs constituting the device.
The present invention is directed to overcoming these and other deficiencies in the art.